1. Field of the Invention
This invention relates to the charging of zinc-smelting blast furnaces with alternate loads of coke and zinc oxide material from a hopper by means of central bell/annular bell charging gear.
2. Description of the Prior Art
In co-pending British Patent Application No. 45252/78 (published as Specification No. 2,009,903 on June 20, 1979) there is described and claimed a method of charging such a furnace whereby coke can be directed primarily toward the furnace centre or primarily toward the furnace walls as required, depending upon whether maximum fuel economy or wall-cleaning operation is required. This is achieved by lowering the annular bell through a predetermined fixed distance and either lowering the central bell through a smaller distance (for coke-rich wall charging) or keeping the central bell static or raising or lowering it through a smaller distance (for coke-rich centre charging). A similar procedure is adopted for charging zinc oxide material in the form of sinter or briquettes.
At the time of filing the above-defined patent application, it was not appreciated that another important parameter was the time taken to lower the annular bell through the predetermined fixed distance and more particularly the ratio of this time to the time taken for the hopper contents to completely discharge into the furnace.
It has now been realized that if the discharge time of the hopper contents is greater than the lowering time for the annular bell, then wall-directed charging of the hopper contents is impaired and that it is difficult to obtain consistent distribution of charge between the centre and the walls of the furnace.